Machines for producing such packages are well known. However, before development of the applicant's present invention, all commercially available machines of this type known to the applicant were designed to produce packages of a predetermined length and, in a practical sense, were incapable of being readily adjusted to produce short runs of packages or even single packages of varying length.
Various means are employed in such commercially available machines to change the bag length. In a commonly known type of machine, exemplified in the specification of British patent #1137057, the drive rollers for advancing the tube stock are operated stop/start fashion by a crank mechanism. The throw of the crank can be varied to alter the length of bag produced by the drive rollers. This arrangement is quite unsuitable for quick changes of bag length.
In a commercially available type of plastic bag making machine the drive rollers are also operated stop/start fashion. They are digitally controlled to feed the tube stock a distance determined by punching a desired bag length into a numeric keypad on the machine. Such machines are designed to produce about 100/200 bags per minute so, in day to day operation, changing bag length between each bag or even after a run of few bags would be out of the question.
Bag making machines which are installed at a workstation where goods are packaged at the same time as the bags are made or dispensed can be divided into three different classes:
a. machines which are intended for the high speed packaging of long runs of articles which are mutually identical or of liquids in mutually identical quantifies. Examples of such machines are shown in U.S. Pat. Nos. 3,537,225 (Fields), 4,346,546 (Tasker) and 3,557,526 (Hartmann). PA1 b. the applicant is aware of a single patent, U.S. Pat. No. 3,161,002 (Duns), showing a machine from which bags of varying length can be obtained. PA1 c. machines for dispensing pre-made bags. A machine of this type is disclosed in U.S. Pat. No. 3,908,343. Such machines are not relevant to the present invention.
In the above mentioned patents, the only machine which is intended to produce bags whose length can be varied as each bag is made is shown in the Duns patent. In this machine the bag length is varied by the operator who manually draws off the require length of tube from the tube stock each time a bag is made. It will be clear to those skilled in the an that the remaining patents show machines which are quite unsuitable for quick changes of bag length. That they are all intended for producing long runs of bags of constant length is apparent from the descriptions of the length changing mechanism in each case in combination with the other parts of the machine and the product to be packaged.
In certain circumstances, producers of goods of variable length which require similar packaging would find such machines of substantial commercial benefit. Thus the present invention has particular but not exclusive application to the factory packaging of joints of meat and other articles of somewhat variable size.